1. Field of the Invention
The present invention relates to a self-locking cerebral probe for stereolectroencephalographic exploration, and more particularly, to such a probe which may be used to assist in treating epilepsy or other brain diseases.
2. Prior Art and Technical Considerations
Epilepsy is a chronic disease essentially characterized by a more or less frequent repetition of cerebral attacks resulting from a sudden, excessive and anarchic discharge of some nerve cells within the cerebral shell. This frequently results in more or less violent muscular movements of the entire body of the patient and eventually to a sudden fainting spell. Treatment of epilepsy has always caused serious problems for the specialist, essentially due to the difficulty of correctly defining the epileptogen zone and of consequently obtaining the information necessary for selection of the surgical operation to be performed.
Several schools of thought exist on the methodologies that may be used for accurately locating in the cerebral cortex, that is in the grey substance of the brain, the group or groups of abnormal cells which produce electrical discharges in an anarchic manner according to a still unknown mechanism that provokes the crisis of epilepsy.
The specialists of the principal school ground their diagnosis mainly in the study of the intercritical epileptic activity for locating the epileptogen region. This study includes clinical observation, scalp electroencephalography for measuring the electrical activity of the brain, and surface electrocorticography. Surface electrocorticography consists of opening the skull of the patient, depositing on the portion of the exposed brain several recording probes and then electrically stimulating the brain so as to reproduce an epileptic crisis in the patient.
This methodology, which has already been successful for many patients unfortunately has a low yield and a major drawback of confusing the "irritative" zone, which is the zone in which the epileptic activity originates between crises, with the "epileptogen" zone, which is the zone in which the crisis starts. These two zones may coincide but it is presently not known if this is always the case.
Moreover, this methodology is quite "subjective" because the crises of epilepsy are always of short duration and arouse much emotivity in witnesses. Furthermore, the electrical cerebral activity recorded by electroencephalography amounts to only millionths of a volt and is often distorted because it is picked up through the scalp, skull and tuft membranes of the brain.
From this main school, a new school has formed, particularly since publication of the works of Drs. Talairack and Bancaud, M.D., of Paris.
The specialists of this new school also ground their diagnoses on the study of intercritical epileptic activity for locating the epileptogen zone, but they have developed in a more rigorous manner the presently known methodology. The new school does not consider it sufficient to record the spontaneous crisis in order to locate the epileptogen region, to provide a clinical description of the crisis by witnesses and to provide an intercritical recording of several electroencephalograms. The new school has also proposed recording electroencephalograms while simultaneously recording the crisis audiovisually in order to obtain maximum information and to verify, in particular, if the recorded crises fully corresponds to the usual crisis of the patient. Above all, the new school attempts to determine if there is coincidence in time between the electrical discharges of the cells and the clinical manifestations of the disorder. After anatomoclinical correlations have been made and the diagnosis has been set, the epileptogen zone, also known as the "epileptic center", which is the group of cells responsible for the crisis of epilepsy, may be searched.
In order to accomplish this, it is necessary to investigate thoroughly the region of the brain that is involved. This includes the cerebral cortex extending to the surface of the brain, the depths of the lines of the brain, the interhemispheric face, the orbital faces of the frontal lobes and in the deep portion of the temporal lobe. In other words, places not accessible with a surface corticography.
This investigation is performed in the operating room, using a rigid frame also known as a stereotaxical frame, in which the head of the patient is mounted so that all the subsequent steps of the anatomic study may be performed with the same rigorous precision. The frame first enables realization of a neuroradiologic evaluation by teleradiography, including bilateral cerebral angiography, fractionated pneumoencephalography and positive contrast venticulography, in order to precisely determine the positions of the arteries, veins and other structures that are to be investigated. The frame also enables the introduction of as many probes as necessary, generally 8 to 10 probes, in the brain with a very great precision and security, in order to locate the abnormal cells.
The probes permit recording of cerebral activity in depth, which is known as "stereoelectroencephaplographic recording". The electrophysiologic evaluation obtained after having recorded several provoked crisis and several spontaneous crisis with the cervical probes, permits the specialists to precisely define where the epileptogen zone is located and to select the surgical treatment which is appropriate, either with or without opening of the skull.
This new methodology is more "efficient" than the classical methodology since it results presently in cures on the order of 70% of the cases.
However, this new methodlogy as it has been used to date, presents a drawback in that, for several technical reasons, the stereoelectroencephalographic recording can only be carried out under "acute" conditions because of the rigidity of the probes. By acute recording is meant a recording that is made in the operation room in the following manner: the probes are located under general anesthesia; the patient is then awakened and must hold his head fixed in the frame for a period of from 6 to 8 hours so as to record at least one spontaneous crisis or at least one induced crisis.
It is obvious that these recording conditions are not propitious and that the obtained information is worth less than information that could be obtained under more diversified physiological conditions.